Phar File Format

The phar file format is literally laid out as stub/manifest/contents/signature, and
stores the crucial information of what is included in the phar archive in its
manifest.

The Phar manifest is a highly optimized format that allows per-file
specification of file compression, file permissions, and even user-defined
meta-data such as file user or group. All values greater than 1 byte are stored
in little-endian byte order, with the exception of the API version, which
for historical reasons is stored as 3 nibbles in big-endian order.

All unused flags are reserved for future use, and must not be used
to store custom information. Use the per-file meta-data facility
to store customized information about particular files.